As generally known, the function of cooling towers is to bring cooling water into direct contact with air so as to evaporate water thereby cooling water by the latent heat. Since the cooling water is brought into direct contact with air the cooling towers have greater efficiency of heat transfer than in air cooling heat exchangers which transfer heat by raising only the temperature of air and, as a result, they are small-sized and less expensive to install. Thus, a variety of cooling towers ranging from large size to small size have hitherto been proposed to be launched in practical use for freezing and air conditioning.
Incidentally, as the problems which occur in administering a cooling tower there may be mentioned such troubles as corrosion, scale and sliming which take place in recycling cooling water system. Particularly, in an open type recycling cooling water system a part of the water evaporates in the cooling tower, so that the salts dissolved in the recyclying cooling water are concentrated in the recycle cooling water. On the other hand, calcium, silica and like existing, in the form of ions, in the recycle cooling water cause the generation of scale. These troubles not only lower the efficiency of heat exchange but also impair freezer, piping and the like. The measures taken to avoid such troubles are to effect a blow-down of discharging to the outside of the recycle cooling water a part of the recycling water to retain below a fixed value the contents of salts and other impurities in the recycling water, and to introduce chemicals such as anticorrosive, scale preventing agent and the like.
In the concentration administration of a recycling cooling water system by blow-down and the control by adding chemicals a system is usually adopted in which the conductivity of recycling water is measured, the concentration magnification of the recycling water is computed based on the measurement, and the amount of the blow water is automatically controlled. On the other hand, for the water treatment agents such as anticorrosive and scale preventing agent it is required always to retain a proper concentration in the recycling water, the amount of the water treatment agents introduced for the retention of the proper concentration is determined depending on the blow amount on the basis of the concentration set for retaining the chemicals, scattering loss amount, making-up water amount, etc., and the water treatment agent in an amount set by a chemical introducing apparatus is to be added for making-up the loss.
When water quality is controlled, particularly when chemicals such as anticorrosive, scale preventing agents and the like are introduced, the conductivity of the recycling water in the basin within the cooling tower is periodically computed, and the introducing amount of the chemicals is determined based on the computed data. However, considering that the loss of the recycling cooling water due to transpiration or the like varies depending on the operational condition of the equipment or on seasons, the chemicals must be retained usually above the lower limit concentration wherein they exhibit their effects. From the viewpoints of such retention and of controlling, the chemicals are added periodically (for example, several times a year) so that their concentration may be considerably higher than the concentration thereof in usual use. In this connection, the concentration of the water treatment agent in recycle cooling water is in a state far higher than the lower limit concentration wherein the chemicals demonstrate their effects, and this results in the use of the water treatment agent in a larger amount than practically required. This causes waste of comparatively expensive water treatment agent and an increase of running cost.
If the recycle cooling water transpires and the concentration of the chemicals reaches its upper limit as set, a sensor for conductivity senses said upper limit thereby to start blowing, while if the concentration becomes lower than a differential value smaller than the set upper limit the blowing is stopped. According to conventional methods, the adding quantity of the chemicals has been set irrespective of the blow amount whereas the chemicals in set amounts have been introduced by a pump of introducing an estimation amount irrespective of concentration. When the ambient air is lower in temperature the concentration of the chemicals is higher than a set value. However as the ambient temperature rises, transpiration of the cooling water is increased and thus the concentration of the chemicals is changed. Therefore, a person having knowledge or experience has so far determined the adding amount at the appropriate season. On the other hand, if there is no person who can manage such controlling, the pumping has generally been set on the basis of months of larger loading (transpiration), such as July and August.
Furthermore, in practical operation the cooling water is subject to recirculation or loading so that it cyclically evaporates and scatters from the cooling tower. The quantity of the scattering water varies depending on the profile of structure of the using cooling tower or on the installation place of the cooling tower or weather conditions (such that the installation place is under strong wind or likely to be exposed to strong wind). Therefore, if it is intended to add the water treatment agent proportionally to the blow amount as mentioned above, in the case of a cooling tower of comparatively greater scattering the concentration of the water treatment agent becomes insufficient when the blow amount is less.
Furthermore, conventionally, the initial introduction of the water treatment agent was carried out through human work at the time of starting to use or cleaning the cooling tower. This prevented the equipment from complete automation. Moreover, this kind of equipment is started for use almost at the same period (approximately April or May in Japan) each year, and it is necessary to effect cleaning or maintenance inspection or to initially introduce the water treatment agent at that period, and therefore it is difficult to secure working personnel thus leaving problems still to be solved.